1. Field of the Invention
This invention relates to a laminate having an internal member responsive to stimuli; to an interlayer composite to seal the edge portions of the laminate; optionally to bus bars arranged on the internal member to eliminate hot spots at end portions of the bus bars; to methods of fabricating the laminate using the interlayer composite, and optionally the arrangement of the bus bars, and, in particular, to a heatable transparent laminate, e.g. an automotive windshield having an interlayer composite having a lead assembly to prevent ingress of air into the laminate and to provide external electrical access to bus bars optionally arranged to eliminate hot spots at end portions of the bus bars, and to methods of making the heatable laminate.
2. Discussion of the Technology
Automotive heatable windshields, e.g. of the type disclosed in U.S. Pat. No. 4,820,902 include two glass sheets laminated together by a plastic interlayer, usually a sheet of polyvinyl butyral (“PVB”). A pair of spaced bus bars between the glass sheets are in electrical contact with an electrically conductive member, e.g. a sputtered electrically conductive coating of the type disclosed in European Patent Application No. 00939609.4, applied to a major surface of one of the glass sheets or a plurality of electrically conductive filaments of the type disclosed in U.S. Pat. No. 5,182,431. Each of the bus bars is electrically accessible by an external lead to pass current from a power source through the bus bars and the coating to electrically heat the coating and heat by conduction the inner and outer surfaces of the windshield. The heated windshield surfaces attain a temperature sufficient to remove fog, and melt snow and ice. As can be appreciated, heatable windshields are practical, and in some geographical areas are a requirement, during the winter season.
In the fabrication of commercially available automotive windshields, an electrically conductive coating, usually a sputtered electric conductive coating is applied to a flat piece of glass. The flat piece of glass is cut to provide a blank. A pair of spaced bus bars is provided on the coating by silk-screening an electrically conductive ceramic paste onto the conductive coating as discussed in U.S. Pat. Nos. 4,654,067 and 4,718,932 or by using metal foil bus bars as discussed in U.S. Pat. Nos. 5,418,026; 5,466,911, and 5,850,070. A second glass blank has a black band silk-screened onto the marginal edges. The black band shields the underlying adhesive securing the windshield to the automotive body from ultraviolet (“UV”) radiation that can deteriorate the adhesive and provides an aesthetically pleasing appearance.
The coating and silk screened bus bars are normally applied to a surface of a blank that is designated as the No. 3 surface of the laminated windshield, i.e. the outer surface of the inner glass blank of the laminated windshield as mounted in the vehicle. The black band is normally applied to a surface of a blank that is designated as the No. 2 surface of the laminated windshield, i.e. the inner surface of the outer glass blank of the laminated windshield. The glass blank having the coating and the bus bars, and the glass blank having the black band are each shaped for a contoured windshield. A sheet of plastic interlayer, usually polyvinyl butyral is positioned between the shaped glass sheets (referred to as a “windshield subassembly”). When the bus bars are not silk screened on the coating, e.g. when metal foil bus bars are used, the bus bars are positioned between the interlayer and the coating.
The edges of the windshield subassembly are edge sealed in the usual manner, e.g. moving the windshield subassembly through nipper rolls or placing a vacuum channel around the periphery of the windshield subassembly and pulling a vacuum while heating the windshield subassembly. Thereafter the edge sealed windshield subassembly is placed in an air autoclave; heat and pressure are applied to the edge sealed subassembly to provide a laminated windshield. The seal around the periphery of the edge sealed windshield subassembly is formed to prevent air from moving between the glass sheets during the removal of the vacuum channel after the edge sealing operation and/or during the autoclaving.
For a general discussion regarding heatable windshields reference may be had to U.S. Pat. Nos. 3,789,191; 3,789,192; 3,790,752; 3,794,809; 4,543,466, and 5,213,828.
As can be appreciated, eliminating the silk screening of bus bars eliminates a manufacturing operation and all the limitations associated therewith such as the inventory of silk screens for each windshield design, handling and inventory of the ceramic conductive paste, and maintaining efficient operation of the silk-screening machines. Using metal foil bus bars eliminates the limitations associated with silk screening bus bars; however, there are other limitations in the use of metal foil bus bars. More particularly, the metal foil bus bars are in surface contact with the conductive coating. A lead, usually an extension of the bus bars, extends out of the laminate to provide electrical access to the bus bars. The surface of the lead that is a continuation of the surface of the bus bar in contact with the conductive coating and the adjacent portions of the glass sheet provide an air path. During the removal of the channel from, and/or during the autoclaving of, the edge sealed windshield subassembly air moves through the air path between the glass blanks. As can be appreciated by those skilled in the art of laminating windshields, the air moving between the blanks causes delamination. Depending on the severity of the delamination, the windshield may have to be discarded or replaced.
It would be advantageous therefore to use metal foil bus bars to eliminate the drawbacks of silk screening while eliminating the present drawbacks of metal foil bus bars.